In the case of aircraft with a cabin divided into a plurality of regions, it is generally the desire to be able to all condition each region at a different temperature. For example, economy class can have a different temperature to business class. In a first-class suite the temperature can be individually settable. The temperature in business class is typically centrally preset. However, a passenger can individually set the temperature in the environment of his or her seat, so that the environment of the seat is supplied with colder or warmer air than the rest of the business class region. Through the individual air conditioning of regions of the cabin, it is also possible to take into account different heat loads in the regions.
FIG. 5 illustrates a conventional system for the air conditioning of sub-regions of an aircraft. A central air conditioning unit 102 is supplied with an air flow 104 which is put under a pressure higher than the pressure outside the cabin. Typically, the pressure is approximately 700 to 800 mbar, which corresponds approximately to a height of 2000 m to 3000 m above sea level. The air 104 to be supplied to the central air conditioning unit 102 can be, for example, air 136 recirculated from a cabin or engine bleed air. The central air conditioning unit 102 delivers an air flow 106 at a predetermined temperature. The air flow is distributed to a plurality of lines 108, 112, 114 and 116, where it is supplied to separate heating devices 118, 120, 122 and 124. From the cabin heating device 118 the air flow 128 is supplied to a cabin 126. From the first heating device 120 the air flow 130 is supplied to an environment of a first seat 138. The air flow 132 delivered by a second heating device 122 and the air flow 134 delivered by a third heating device 124 are supplied to a respective environment of a second seat 140 and a third seat 142. A temperature sensor 150 is provided in the cabin and a respective temperature sensor 144, 146 and 148 is arranged in the environment of the seats 138, 140 and 142. The temperature sensors 150, 144, 146 and 148 and a control device (not shown) control the assigned heating devices 118, 120, 122 and 124 in such a manner that air at a desired temperature is supplied to the cabin 126 or the regions of the seats 138, 140 and 142.
The central air conditioning unit 102 has to provide the air flow 106 at the temperature corresponding to the lowest temperature desired in the cabin 126 and the regions of the seats 138, 140 and 142. If a temperature substantially lower than the temperature desired in the cabin 126 is desired in one of the regions of the seats 13S, 140 and 142, the heating device 118 for the cabin has to expend a large amount of energy in order to bring the air flow 108 to the desired temperature. If the heating device 118 is an electrical heating device, this has to expend a relatively large amount of electrical energy. In an aircraft, loads which consume a large amount of electrical energy are undesirable since the electrical energy has to be obtained at relatively high cost and with relatively high losses from rotational energy of the turbines. Alternatively to this, the heating device 118 can have trim valves which supply the engine bleed air. However, this requires relatively large bleed air ducts which have to be routed through the cabin. This is undesirable since additional space is required for the bleed air ducts and the mass of the aircraft increases.